Enhancement of strength and transport properties of a novel preplaced aggregate fiber reinforced concrete by adding waste polypropylene carpet fibers

Preplaced aggregate concrete (PAC), also known as two-stage concrete (TSC), is a particular type of concrete that is produced by placing coarse aggregates in a form and voids amongst them are then injected with a flowable grout. The preplaced aggregate fiber reinforced concrete (PAFRC) is new developed concrete, with a unique mixture of coarse aggregates and short fibers that are premixed and preplaced in the formwork and injecting grout into the voids of the aggregate mass. The current study develops the concept of a new PAFRC reinforced with waste polypropylene (PP) carpet fibers and investigate its strength and transport properties. Palm oil fuel ash (POFA) was used as partial cement replacement. Six PAFRC mixes with fibers varying from 0 to 1.25% with a length of 30 mm were made by the gravity method. Another six batches with the similar fiber dosages were made, where the pumping method was used to inject the grout into the voids between the aggregates. The results showed that by adding carpet fibers, the compressive strength of PAFRC specimens reduced. However, the PAFRC specimens revealed a notable enhancement in the tensile strength values. Moreover, water absorption, sorptivity, and chloride penetration depth were reduced for POFA-based PAFRC specimens reinforced with carpet fibers. The study revealed that the carpet fibers are potential to be used in PAFRC by developing the transport and strength properties.